1. Field of the Invention
The present invention generally relates to methods and systems for preparing a copper containing substrate for analysis. Certain embodiments relate to methods and systems for removing a portion of a copper structure on a substrate using an etch chemistry in combination with an electron beam.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a semiconductor wafer and then separated into individual semiconductor devices.
As the dimensions of advanced semiconductor devices continue to shrink, the presence of defects in the semiconductor devices increasingly limits the successful fabrication, or yield, of the semiconductor devices. For example, incompletely filled vias formed on a wafer during deposition may cause an open circuit in, or complete failure of, one or more semiconductor devices formed in subsequent processing. Accordingly, defect detection, or “inspection,” of semiconductor wafers is and will continue to be of significant importance in semiconductor development and manufacturing. In addition, review and analysis of defects is of significant importance in determining the cause of defects such that they may be corrected.
The ability to remove device film layers (“de-layer”) or structures at select locations on a wafer in a localized and controllable fashion is critical for defect review and analysis during the device fabrication process. For example, removing a device film layer may allow a better view of a defect, particularly a subsurface or partially subsurface defect. In addition, removing a device film layer may enable analysis of the defect composition to be performed with less interference from the surrounding film layer.
Current techniques for de-layering of a substrate utilize ion beam etching, laser ablative etching, or mechanical abrasion using a micro-tip. Focused ion beam etching utilizes gallium ions to stimulate etching. Laser ablative techniques utilize lasers to heat the surface of the substrate to cause chemical and thermal reactions that remove the films. The mechanical abrasion technique uses micro-tips to remove the films around the defect.
Of the current techniques, ion beam etching is the most mature technique used to de-layer devices. However, when using an ion beam to stimulate etching, gallium ions from a source are implanted into the films, which can lead to changes in the optical, electrical, and mechanical properties of the etched features and the surrounding areas. The presence of gallium ions in the device can limit further processing of the device and the wafer in the fab, which would result in scrapping the entire wafer. In addition, during focused ion beam etching, the etched material may be deposited in the surrounding areas on the wafer. The other techniques currently used for de-layering of a substrate also have several disadvantages. For example, the laser ablative technique has low etch selectivity. In addition, the mechanical abrasion method has limited applications to certain large defects and films.
Accordingly, it would be advantageous to develop methods and systems for preparing a substrate for analysis by removing a portion of a structure or de-layering a structure on the substrate, which do not destroy or contaminate the substrate or the structure. In particular, it would be advantageous to develop methods and systems that can be used to remove a portion of a copper structure on a substrate such that the copper structure or defect thereof can be analyzed.